lvon] xhk hares and tiii:ir alli1':s 437 



relatively small, the Itinare narrow, the internal half of the cuneiform 

 larger, which presents a well-developed convex facet for articulation 

 with the ulna, as mentioned ahove. The os centrale is (juite large, 

 and not flask-shaped. The os magnum is rather small. A small os 

 vesalianum is present. 



The metacarpus and ])halanges of Ocluihnia are (luile like the 

 same structures in Lcpiis. The second and fourth metacarpals are 

 nearly as long as the third. The width of the three middle meta- 

 carpals is contained ahout one and a half times in the length of the 

 third metacarpal. 



Pchns and Lower Extremity. — The most striking feature of the 

 pelvis of Ochotona is the ahsence of the symphysis ])ubis. The 

 ])ubic bones are widely separated from one another but are connected 

 by a ligament. As none of the few available skeletons are sexed, it 

 is barely possible that this character is sexual. The os innominatum 

 is rather long and slender, the ilium rather thick, its ventral third 

 separated from the dorsal two-thirds by a well marked ridge, which 

 terminates anteriorly and ventrally in a well-marked, recurved, 

 pointed spine. The thyroid foramen is ovoid, its narrow end directed 

 forward toward the acetabulum. 1 he horizontal ramus of the pubis 

 is very short, the descending ramus long, directed obliquely backward 

 and downward. 



The femur of Ochotona has the same general character that it has 

 in Lepus, but is relatively thicker and heavier. The third trochanter 

 is much reduced in size, the lesser trochanter relatively larger. The 

 fossa behind the great trochanter is not so deep as in Lepus. The 

 length of the femur is a trifle less than that of the tibia. 



The tibia and fibula (pi. xcix, 6, 7) of Ochotona are similar in all 

 respects, except in absolute size, to these bones in Ronierolagiis. The 

 fibula fuses with the tibia at the middle of the latter bone. The inner 

 surface of the lower part of the shaft of the tibia is concave. 



The tarsus of Ochotona is generally like that of Lepus. The 

 middle cuneiform, however, is fused with the base of the second 

 metatarsal. The basal width of the metatarsals is contained one 

 and a half times in the greatest length of the metatarsals. There 

 is a large sesan:oid bone at the platar surface of the base of the fifth 

 metatarsal. This bone is lacking in the Leporid^e, but is represented 

 by a prominent tubercle on the fifth metatarsal in the same situation. 



The skulls of Ochotona available for study are a heterogeneous lot, 

 capable of being placed in three distinct groups, described below as 

 subgenera. 



